Cm-2 Day-1 Research Articles

SPS technique for ionizing radiation source fabrication based on dense cesium-containing core.

The work presents a novel method for fabrication of the high-quality ionizing radiation source (IRS), which is promising to replace unsafe commercial products based on 137CsCl prohibited by IAEA. Spark plasma sintering (SPS) technique has been applied to produce dense ceramic and glass-ceramic matrixes from Cs-containing (˜13.5 wt.%) zeolite yielding in non-dispersible cores sealed in the container of radiation-resistant steel (J93503, US standard). One-stage SPS regimes to provide high-quality product have been optimized: sintering temperature <1000 °C, heating and holging duration 13 and 5 min, respectively, pressure 24.5 MPa. XRD, SEM, EDX, BET, XFS and solid-state MAS NMR 133Cs methods prove exceptional physico-chemical and mechanical characteristics of the obtained materials, namely: density 99.8% from theoretical, compressive strength ˜477 MPa, leaching rate 10-4-10-6 g cm-2 day-1. Results of the investigation can be promising for fabrication of the IRS cores on a large scale as done for similar Russian products RSL, IGI-C, M37C, GID-C.

Atomistic and continuum scale modeling of functionalized graphyne membranes for water desalination.

Recent theoretical and experimental studies reported ultra-high water permeability and salt rejection in nanoporous single-layer graphene. However, creating and controlling the size and distribution of nanometer-scale pores pose significant challenges to application of these membranes for water desalination. Graphyne and hydrogenated graphyne have tremendous potential as ultra-permeable membranes for desalination and wastewater reclamation due to their uniform pore-distribution, atomic thickness and mechano-chemical stability. Using molecular dynamics (MD) simulations and upscale continuum analysis, the desalination performance of bare and hydrogenated α-graphyne and γ-{2,3,4}-graphyne membranes is evaluated as a function of pore size, pore geometry, chemical functionalization and applied pressure. MD simulations show that pores ranging from 20 to 50 Å2 reject in excess of 90% of the ions for pressures up to 1 GPa. Water permeability is found to range up to 85 L cm-2 day-1 MPa-1, which is up to three orders of magnitude larger than commercial seawater reverse osmosis (RO) membranes and up to ten times that of nanoporous graphene. Pore chemistry, functionalization and geometry are shown to play a critical role in modulating the water flux, and these observations are explained by water velocity, density, and energy barriers in the pores. The atomistic scale investigations are complemented by upscale continuum analysis to examine the performance of these membranes in application to cross-flow RO systems. This upscale analysis, however, shows that the significant increase in permeability, observed from MD simulations, does not fully translate to current RO systems due to transport limitations. Nevertheless, upscale calculations predict that the higher permeability of graphyne membranes would allow up to six times higher permeate recovery or up to 6% less energy consumption as compared to thin-film composite membranes at currently accessible operating conditions. Significantly higher energy savings and permeate recovery can be achieved if higher feed-flow rates can be realized.

Quantitative Analysis of Greenhouse Kohlrabi (&lt;i&gt;Brassica oleracea var. gongylodes &lt;/i&gt;L.) Growing

This study were carried out to of different sowing time in order to determine the effects on plant growth of kohlrabi cultivation under Samsun condaitions during the autumn growing periods in unheated greenhouse. Four different seed sowing times (1st September, 15th September 1st October, 15th October), two different kohlrabi cultivars (Kolibri F1 and Korist F1) and two mulch applications (mulch covered and uncovered) were used in this study.The plant growth parameters analyzed (total plant dry weight, leaf area ratio, specific leaf area, net assimilation rate and relative growth rate) were found statistically significant (p&lt;0.05). The highest total plant dry weight (114.1 g) was obtained from mulch application and 1st September seed sowing time. The highest leaf area ratio value were obtained in both mulch application the Kolibri F1 variety grown on October 15th. The highest net assimilation rate (0.65 g cm-2 day-1*1000) and relative growth rate (0.0090 g g day-1) were obtained from mulch covered plants grown in Kolibri varieties during September 1st. As a result, in this study higher dry matter accumulation was achieved by 1st September seed sowing times in vegetable growing in the last season in the greenhouse. In this way, the plants have successfully grown up and increased their productivity by entering the winter months, when the temperature and light intensity are decreasing.

Macromolecular Design Strategies for Preventing Active-Material Crossover in Non-Aqueous All-Organic Redox-Flow Batteries.

Intermittent energy sources, including solar and wind, require scalable, low-cost, multi-hour energy storage solutions in order to be effectively incorporated into the grid. All-Organic non-aqueous redox-flow batteries offer a solution, but suffer from rapid capacity fade and low Coulombic efficiency due to the high permeability of redox-active species across the battery's membrane. Here we show that active-species crossover is arrested by scaling the membrane's pore size to molecular dimensions and in turn increasing the size of the active material above the membrane's pore-size exclusion limit. When oligomeric redox-active organics (RAOs) were paired with microporous polymer membranes, the rate of active-material crossover was reduced more than 9000-fold compared to traditional separators at minimal cost to ionic conductivity. This corresponds to an absolute rate of RAO crossover of less than 3 μmol cm-2 day-1 (for a 1.0 m concentration gradient), which exceeds performance targets recently set forth by the battery industry. This strategy was generalizable to both high and low-potential RAOs in a variety of non-aqueous electrolytes, highlighting the versatility of macromolecular design in implementing next-generation redox-flow batteries.

PRODUCTIVITY OF HAIRY WATER LILY (Nhymphaea pubescens Will.) SEEDS IN SOUTH KALIMANTAN’S BACKSWAMPS BASED ON LINEAR MODEL

The study on the productivity of water lily seeds in South Kalimantan’s backswamps using Wageningen method and the interview with middle traders could give more information about water lily as food commodity. Rainfall pattern in Tabalong, Hulu Sungai Utara (HSU) and Hulu Sungai Selatan (HSS) regencies is like U letter. U type is sensitive with Monsoon. This Monsoon area is affected by easterly wind and local wind. When the sun is at the south side in October to March, the Monsoon moves from west to south east, and in the other way around in April to September, the wind moves from south east to west. In April, the height of water level in some different areas was the same. The highest water level was in Paharangan subdistrict that could reach more than 100 cm and the lowest was in Hambuku subdistrict, about 80 cm. Based on the interview with middle traders, it was found out that in Hambuku subdistrict and its surrounding area, there was about 1.0 to 1.7 t/ha of water lily seeds each period. In Ampukung, Hambuku and Paharangan subdistricts, the water lily seeds were about 1.121 t/ha, 1.057 t/ha and 0.653 t/ha, respectively. If the paddy fields in Tabalong, HSU and HST regencies are 10,683 ha, 21,2252 ha, and 18,763 ha, respectively, those areas potentially can yield about 11,976.661 t/ha, 224,456.2 t/ha and 12,254.6778 t/ha. Whereas, based on radiation (Rg), the photosynthetically active radiation on very clear days (Ac), in cal cm-2 day-1, and daily gross photosynthesis rate of crop canopies on very clear days (bc) in kg ha-1 day-1 for Pm = 20 kg CH2O ha-1 hr-1, it showed that the yield of hairy water lily seeds in Ampukung, Hambuku and Paharangan subdistricts was 1.1560 t/ha, 1.1425 t/ha and 1.1021 t/ha, respectively. Hairy water lily naturally grows with seeds in soil and water in paddy field, so it can grow, develop, and produce seeds. Therefore, agronomical technique is important for further study.

Early detection of injuries in leaves of Clusia hilariana Schltdl. (Clusiaceae) caused by particulate deposition of iron

This study aims to evaluate the prognostic value of microscopic parameters of asymptomatic leaves of Clusia hilariana Schltdl. subjected to particulate deposition of iron (2.14 mg cm-2 day-1) for 45 consecutive days. Samples of young and expanded leaves without symptoms were collected and subjected to light and scanning electron microscopy techniques. The height of the epidermal cells on both surfaces of the leaf and the thickness of the hypodermis, the chlorophyll parenchyma, and the leaf blade were measured. Micromorphological injury occurred in the abaxial surface of young leaves and on both surfaces of expanded leaves. Erosion of the epicuticular wax and cuticle rupture were frequent on the adaxial surface, while on the abaxial surface of both leaves there was a loss of sinuosity on the anticlinal wall of the epidermal cells, stomatal deformity and obstruction. Micromorphometric alterations were seen in all leaf tissues except in the height of epidermic cells, probably due to the thick cuticle and prominent cuticular flanges. The highest difference in thickness of the leaf blade was seen in young leaves of plants subjected to SPMFe, indicating greater sensibility to particulate iron in comparison to the expanded leaves. The micromorphological and micromorphometric alterations in the leaf blade of Clusia hilariana Schltdl. showed the prognostic potential of these tools on the evaluation of impacts caused by the deposition of particulate matter, especially in the 'Restinga' natural vegetation, where the exposure is increasing due to the presence of iron ore industry in their surroundings.

Effects of phosphorus application on root respiration and heterotrophic microbial respiration in Acacia mangium plantation soil

We investigated the effects of phosphorus (P) application on root respiration (RR) and heterotrophic microbial respiration (MR) in an Acacia mangium plantation using a trenching method. Mean RR was 0.46g Cm-2 day-1 in a non-P-applied plot, which accounted for 16% of total soil respiration, exhibiting a lower RR value and proportion of total soil respiration compared with previous studies. Mean MR was 2.41g Cm-2 day-1, accounting for 84% of the whole soil respiration. P application significantly (P <0.01) increased the mean RR from 0.46 to 0.88g Cm-2 day-1. Applied P was readily absorbed by acacia trees, which was inferred from the lower available P and total P in non-trenched plots compared to the trenched plots, and it is likely that the absorbed P stimulated root activities and RR. P application also significantly (P <0.001) increased the mean MR from 2.41 to 2.89g Cm-2 day-1, probably because P application relieved the P shortage and stimulated microbial organic matter decomposition. Our study suggests that when assessing the effects of P fertilization on C cycling in forest plantation, we should take account of the effects on organic matter decomposition and soil respiration, not only the effects on C sequestration by trees.

Four-year monthly sediment deposition on turbid southwestern Atlantic coral reefs, with a comparison of benthic assemblages

High sedimentation is often related to stress in coral reef communities. Most southwestern Atlantic reefs are characterized by high sedimentation. However, there are no temporal series of sediment deposition rates. We evaluated sediment deposition, the sediment carbonate composition and coral and zoanthid covers on six reefs in Brazil over four-years. Sediment deposition rates varied from near zero to 233 mg cm-2 day-1, with peaks between August and December, and yearly averages ranging from nine to 104 mg cm-2 day-1. Deposition rates presented site-specific correlations with wind, indicating that resuspension must be a major factor. The presence of carbonates varied from 38% to 90%, with two sites showing seasonal differences. Benthic communities were fairly similar among sites, but the analyses suggested particular frequencies at each site. There was no significant correlation between sediment and benthic communities. However, Palythoa caribaeorum usually occur in high sediment deposition areas. Our results did not corroborate previous data that suggested that a 10 mg cm-2 day-1 would be a "critical limit for coral survival". Some coral reefs may be associated with high sedimentation environments including carbonatic fractions, but which does not per se hinder the development of southwestern Atlantic coral reef communities.

Evaluation of Nutrient Release from Sediments of Artificial Lake

This study examined nutrient fluxes between sediment and water with a laboratory-scale benthic chamber. This research targeted an artificial lake that had undergone water-quality problems. Two sites at Lake Asan, Site A in the vicinity of the dam and Site B at the inflow of the lake, were selected and characteristics of the sediments and their influence on the water quality of the lake were evaluated. Most of the inorganic phosphorus in the study area was in the form of apatite and nonapatite phosphorus (91.9% of Site A, 83.3% of Site B). Site B, with a fast-stream velocity, had larger particle size, smaller nutrient level, and smaller amounts of inorganic phosphorus than Site A. The benthic chamber experiment showed that overall fluxes of Site A were as follows: ammonia is 0.003 μmol cm-2 day-1, nitrate is -0.067 μmol cm-2 day-1, and phosphate is 1.049 nmol cm-2 day-1. Site B showed an increase in phosphate concentration after a dissolved oxygen (DO) drop (<3 mg/l), which resulted in smaller negative...

Synthetic calcium aluminosilicate as a matrix for radioactive waste immobilization

The dependence of the total leach rate of monoliths with deionized water at 90°? on the keeping time (MCC-1 test) was measured. The monoliths were formed by cold pressing (25°C, 500 MPa, 2 min) of an air-dry powder of synthetic calcium aluminosilicate (SCAS) with added 10, 20, or 30 wt % simulated radioactive waste (SRW) of the composition typical of radioactive and nonradioactive wastes from a closed nuclear cycle. The leach rate of the SCAS-SRW monolith is 6.7 × 10-7, 7.2 × 10-7, and 8.3 × 10-7 g cm-2 day-1 at an SRW content of 10, 20, and 30 wt %, respectively.

Characterization of Pollen Dispersion in the Neighborhood of Tokyo, Japan in the Spring of 2005 and 2006

The behavior of Japanese cedar (Cryptomeria japonica) and Japanese cypress (Chamaecyparis obtusa) pollens in an urban area was examined through the measurements of the dispersion characteristics at the various sampling locations in both outdoor and indoor environments. Airborne pollens were counted continuously for three months during the Japanese cedar pollen and Japanese cypress seasons in 2005 and 2006 by the use of Durham's pollen trap method in and around Tokyo, Japan. The dispersion of pollens at the rooftop of Kyoritsu Women's University was observed to be at extremely high levels in 2005 compared with previously reported results during the past two decades. As for Japanese cedar pollen, the maximum level was observed as 440 counts cm(-2) day(-1) on 18 March 2005. Japanese cypress pollen dispersed in that area in the latter period was compared with the Japanese cedar pollen dispersions. The maximum dispersion level was observed to be 351 counts cm(-2) day(-1) on 7 April 2005. Total accumulated dispersions of Japanese cedar and Japanese cypress pollens were 5,552 and 1,552 counts cm(-2) for the three months (Feb., Mar. and Apr.) in 2005, respectively. However, the dispersion of both pollens in 2006 was very low. The total accumulated dispersions of Japanese cedar and Japanese cypress pollens were 421 and 98 counts cm(-2) for three months (Feb., Mar. and Apr.) in 2006, respectively. Moreover, the pollen deposition on a walking person in an urban area showed that the pollen counts on feet were observed to be extremely high compared with the ones on the shoulder, back and legs. These findings suggested that pollen fell on the surface of the paved road at first, rebounded to the ambient air and was deposited on the residents again. Furthermore, the regional distribution of the total pollen dispersion in the South Kanto area was characterized on 15-16 March 2005 and on 14-15 March 2006. Although the pollen levels in 2005 were much higher than in 2006, it was commonly observed that higher pollen counts existed in the outlying areas. That is, the pollen counts in an urban area were confirmed to be at a lower level. As for the indoor dispersion of pollens, two cases were evaluated. At the lobby of the main building of Kyoritsu Women's University, the averaged ratio of the indoor to the outdoor pollen count is 4.1%. Another case was at the hospital building of a medical school. The pollen dispersion in the indoor environment was also observed to be low. It was concluded that the indoor pollen would be mainly carried from the outer environment by the movement of air.

Cutaneous water loss and lipids of the stratum corneum in house sparrowsPasser domesticusfrom arid and mesic environments

Birds that live in hot, dry environments must balance water intake with losses in order to maintain water homeostasis. The outer layer of the integument, called the stratum corneum (SC), consists of corneocytes embedded in a matrix of lipids. The SC serves as a barrier to water vapor diffusion through the skin. We measured cutaneous water loss (CWL) in two populations of house sparrow Passer domesticus L., one living in a desert environment in Saudi Arabia, and another living in a mesic environment in Ohio, USA. We found that CWL rates at 30 degrees C were lower in desert individuals (11.9+/-2.2 mg H(2)O cm(-2) day(-1); N=11) than in mesic birds (16.0+/-2.6 mg H(2)O cm(-2) day(-1); N=14). We hypothesized that changes in the lipid composition of the SC could affect CWL. We analyzed four classes of lipids in the SC: ceramides, cerebrosides, cholesterol and free fatty acids, by thin layer chromatography. Compared to mesic sparrows, desert birds had a higher amount of ceramides (49.2+/-10.3 mg g(-1) SC dry mass in Saudi Arabia; 38.2+/-18.0 mg g(-1) SC dry mass in Ohio) and cerebrosides (101.2+/-48.9 mg g(-1) SC dry mass in Saudi Arabia; 56.5+/-34.0 mg g(-1) SC dry mass in Ohio), and a lower percentage of cholesterol (4.1+/-3.6% in Saudi Arabia; 5.4+/-2.5% in Ohio) in their SC. Although CWL was lower in sparrows from Arabia, and lipid composition of their SC differed, we could not detect differences between rates of water loss through non-living skin attached to glass vials (46.0+/-15.7 mg H(2)O cm(-2) day(-1) for sparrows in Saudi Arabia; 45.8+/-27.2 mg H(2)O cm(-2) day(-1) for sparrows in Ohio). These results suggest that biological control mechanisms interact with layers of lipids in the stratum corneum to adjust CWL to the environment.

Geoceramic Matrices for Immobilization of Nonpartitioned Radioactive Wastes

Immobilization of radioactive wastes (RW) containing large amounts of process alkalis in ceramic matrices based on acid and basic rocks is studied. Immobilizing characteristics of samples with an RW content of 15% are obtained. The best geoceramic matrices are characterized by the forward leaching rates with double-distilled water of ∼1 × 10-4 and ∼1 × 10-5 g cm-2 day-1 for Sr and Cs, respectively, and the steady-state leaching rate of about 2 × 10-6 g cm-2 day-1. Possible fixation mechanisms of the radionuclides in the matrices studied are discussed. Comparative analysis of properties of the geoceramic matrices and borosilicate and some other existing matrices for RW immobilization makes it possible to recommend some kinds of the geoceramics as matrices for immobilization of nonfractionated intermediate- and high-level radioactive wastes.

COMPARISON OF PARTICLE LUNG DOSES FROM THE FINE AND COARSE FRACTIONS OF URBAN PM-10 AEROSOLS

The U.S. Environmental Protection Agency (EPA) recently revised the national ambient air quality standards to include a new PM-2.5 particulate standard. We examine the contributions of fine (PM-2.5) and coarse (PM-2.5 to-10) fraction of typical urban aerosols to particle doses in different lung airways resulting from 24-h exposure to the standard concentration of 150 mug m-3. The aerosol is assumed to have a bimodal lognormal mass distribution with mass median diameters of 0.2 and 5 mum, and geometric standard deviation of 1.7 and 57% of the mass in the fine (PM-2.5) mode. The daily mass dose from exposure to 150 mug m-3 of PM-10 in the nasopharyngeal (NPL) region is 20-51 mug day-1 (1.5% of inhaled fines) and 377-687 mug day-1 (30% of inhaled coarse), respectively, of fine and coarse mass filtered in the nose. Similar daily mass doses from fine and coarse fractions, respectively, to the tracheobronchial (TBL) region are 28-38 (1.5%) and 40-52 (4%) mug day-1 and to the pulmonary (PUL) region are 18-194 (6%) and 32-55 mug day-1 (2%). The daily number dose in the NPL region is 5-15 x 108 (0.06% of inhaled fines) and 5-10 x 106 day-1 (13% of inhaled coarse) respectively, of fine and coarse particles. Similar number doses to the TBL region are 2.2-3.1 x 1010 (2%) and 7.1-11.1 x 105 (2%) day-1 and to the PUL region are 1.6-16.7 x 1010 (9%) and 2.9-17.0 x 105 (3%) day-1. The daily surface mass dose (mug cm-2 day-1) from coarse fraction particles is large in generations 3-5. The daily number dose (particles day-1) and surface number dose (particles cm-2 day-1) are higher from the fine than the coarse fraction, by about 103 to 105 times in all lung airways. Fine fraction particles result in 10,000 times greater particle number dose per macrophage than coarse fraction particles. Particle number doses do not follow trends in mass doses, are much larger from fine than coarse fraction, and must be considered in assessing PM health effects. For the assumed fine fraction ratio of 0.57, the estimated increase in protection from the new PM-2.5 standards is a 25% and 47% lower dose, respectively, at the 24-h and annual standard in comparison with the respective PM-10 standards. The mass fraction in the fine mode depends upon the local sources, will vary with different extents of control of various source types, and will influence the choice of control strategy to meet the revised standard.

第四紀後期の海洋環境と生物生産 外洋域の沈降粒子 堆積粒子からの古海洋の復元のために

Bottom sediments in the open sea mainly originate from sinking particles. Therefore it is very important to investigate chemical properties, seasonality and interannual variability of sinking particles in order to reconstruct paleoenvironments in more detail. Data sets on total, carbonate, organic matter, and biogenic opal fluxes which were measured for more than 5 months are compiled from various areas of the world ocean. Mean total fluxes vary from 0.1 to 16.7 mg Cm-2 day-1 They reflect primary productivity. The enhanced values are observed in arctic, subarctic and equatorial upwelling regions. In general they decrease from coastal region to open sea. Although mean carbonate and biogenic fluxes generally reflect primary productivity, biogenic opal fluxes fluctuated more than carbonate fluxes. Carbonate and biogenic opal are dissolved in the deep sea, therefore it needs much efforts to reconstruct original assemblages of biogenic skeletons.Particle fluxes are affected by river input and upwelling induced by Asian monsoon, upwelling in coastal and equatorial regions, sea ice formation, and volcanic eruption. Long term sediment trap experiments evaluate the surface to the deep sea and/or seafloor, which is one of the most important subjects for understanding paleoenvironments.

Thorium isotopes as indicators of scavenging rates in the Venice Lagoon

The naturally occurring thorium isotopes 228Th and 234Th, produced in sea water from decay of 228Ra and 238U, respectively, were used to estimate the rate of scavenging onto particle surfaces and the rate of removal of particles from the water column of the Venice Lagoon. Large water samples (1000-2000 L) were collected at three sites in the shallow (&lt;1 m) waters of the lagoon. Samples were pumped through two 0.5-μm wound filter cartridges to remove particles and then through two MnO2-impregnated cartridges to extract dissolved Th. Activities of particulate 234Th ranged from 510 to 1335 μBq L-1 and dissolved 234Th was &lt;350 μBq L-1. Relative to calculated 238U activities in the lagoon, the 234Th data yielded mean residence times as short as 2 h for the scavenging of dissolved 234Th onto particles and 12 h for the removal of particulate 234Th. Resuspension rates of 0.6 to 8 mg cm-2 day-1 were estimated from the data on dissolved and particulate 234Th, these values being comparable to those determined by sediment traps (1.8-9.5 mg cm-2 day-1) at the same sites. These results suggest that Th and other similarly reactive trace metals are removed rapidly from the waters of the Venice Lagoon to the sediments.

Some comparative studies of sulfate metabolism in Merino sheep genetically different in wool production

Several aspects of sulfate metabolism were compared in sheep from two selection flocks, selectively bred for either high (Fl+) or low (FI-) clean fleece weight per head. These were studied within a 23 factorial design: 2 flocksx2 levels of formaldehyde treated casein in diet (0 or 80 g day-1)x2 levels of subcutaneous L-thyroxine (0 or 1 mg day-1) with 4 sheep per cell. The treatments influenced the rates of wool growth and the output of sulfur in wool (P &lt; 0.05), but with interactive effects (P &lt; 0.05). The F1+ sheep produced 24 and 32 8g sulfur in wool cm-2 day-1at the midside when consuming the control and casein supplemented diet. The outputs of sulfur in wool by F1- sheep consuming these two diets were 16 and 17 8g cm-2 day-1. The thyroxine treatment increased the rate of growth of wool by 11% (P &lt; 0.05), but did not increase average fibre diameter or the sulfur content of wool. Sulfate was cleared more rapidly (P &lt; 0.05) from the plasma of sheep consuming the casein supplemented diet, with a rate constant of 0.134 h-1, compared to 0.099 h-1for the control sheep. The rate constants for Fl+ and F1- sheep were 0.102 and 0.131 h-1 respectively (P &lt; 0.05). The concentration of sulfate in plasma was similar in all treatment groups: 1.3 mmol L-1The differences in the clearance of sulfate from plasma were reflected in similar differences in the proportion of the injected 35S-sulfate excreted in urine during the following 24 h. The sheep of the F1- flock and those consuming the casein-supplemented diet excreted significantly greater proportions of the injected 35S in urine (P &lt; 0.05). In a second experiment, adult sheep (n = 24), the progeny of F1+ or F1- rams mated with a flock of medium wool Merino ewes, were randomly allocated to a low (c. 0.8 maintenance, 1 g sulfur day-1) or high (c. 2xM, 3 g sulfur day-1) dietary regime. [35S] sodium sulfate was again injected intravenously. There were no significant differences between the genetic groups for (i) sulfate concentration in plasma, (ii) total and net rates of irreversible loss of sulfate from plasma, (iii) the proportion of the injected [35S] sodium sulfate excreted in urine, (iv) the proportion of the excreted 35S present in urine as sulfate, and (v) the quantity of sulfate excreted in urine daily. However, the dietary treatments significantly influenced all these traits, except the concentration of sulfate in plasma. The direction of these effects was consistent with the proposition that sheep regulate excretion of sulfate from kidneys to maintain homeostasis of sulfate within the body. The smaller phenotypic difference in wool production between the two half-bred flocks in the second experiment, probably limited the chances of detecting any differences in the metabolism of sulfate.

Leaf dynamics and standing stocks of intertidal Zostera noltii Hornem. and Cymodocea nodosa (Ucria) Ascherson on the Banc d'Arguin (Mauritania)

Leaf dynamics and standing stocks of intertidal seagrasses were studied in the Baie d’Aouatif (Parc National du Banc d’Arguin, Mauritania) in April and September 1988. Standing stocks of Zostera noltii Hornern, suggest a unimodal seasonal curve similar to what is found for populations at higher latitudes. Also, leaf growth rates (0.03 cm2 cm-2 day-1 on average) were similar to those found at higher latitudes in these months. Variation in leaf loss over tidal depth, time and different locations in the Baie d’Aouatif was larger and more often significant than variation in leaf growth. In general, Z. noltii beds in the Baie d’Aouatif had comparable leaf growth rates and standing stocks. In both months losses were almost always higher than or equal to growth.

Potential denitrification rates in acid soils under pine forest.

Potential rates of N2O production and N2O reduction associated with denitrification were measured from two Dutch soil samples under pine [Pinus] forest, with pH (H2O) 3.6 and 3.8. Undisturbed cores of the surface 15 cm litter and Ah layer were incubated for several weeks in closed pots, of which the gas phase was examined by gas chromatography for O2, CO2, N2O and C2H2. Under anoxic conditions created by soil respiration, average N2O-N production rates in samples from these soils ranged from 9 to 15 mu g cm-2 day-1 and average N2O-N reduction rates from 3 to 6 mu g cm-2 day-1. Rates of N2O production and N2O reduction were measured at two initial nitrate concentrations: N2O production rates were almost the same, but N2O reduction seemed to be delayed by the presence of nitrate. The results indicate that anoxic denitrification peaks might reduce about 1 kg nitrate-N per ha per day in the upper layer of these soils to N2O and/or N2. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Bacterial secondary production on vascular plant detritus: relationships to detritus composition and degradation rate.

Bacterial production at the expense of vascular plant detritus was measured for three emergent plant species (Juncus effusus, Panicum hemitomon, and Typha latifolia) degrading in the littoral zone of a thermally impacted lake. Bacterial secondary production, measured as tritiated thymidine incorporation into DNA, ranged from 0.01 to 0.81 microgram of bacterial C mg of detritus-1 day-1. The three plant species differed with respect to the amount of bacterial productivity they supported per milligram of detritus, in accordance with the predicted biodegradability of the plant material based on initial nitrogen content, lignin content, and C/N ratio. Bacterial production also varied throughout the 22 weeks of in situ decomposition and was positively related to the nitrogen content and lignin content of the remaining detritus, as well as to the temperature of the lake water. Over time, production was negatively related to the C/N ratio and cellulose content of the degrading plant material. Bacterial production on degrading plant material was also calculated on the basis of plant surface area and ranged from 0.17 to 1.98 micrograms of bacterial C cm-2 day-1. Surface area-based calculations did not correlate well with either initial plant composition or changing composition of the remaining detritus during decomposition. The rate of bacterial detritus degradation, calculated from measured production of surface-attached bacteria, was much lower than the actual rate of weight loss of plant material. This discrepancy may be attributable to the importance of nonbacterial organisms in the degradation and loss of plant material from litterbags or to the microbially mediated solubilization of particulate material prior to bacterial utilization, or both.